KR20040037166A - Display system comprising a vedeo processor - Google Patents

Abstract

Display system 10 includes a cathode ray tube (CRT) feedback current replacement circuit 20 for simulating cathode feedback current directly from the red, green and blue output biases of the drive signal of video processor 13. In addition, display system 10 applies vertical blocking to drive stage 16 when bias is applied so that these biases will not be visible during vertical underscan conditions. Shifting the generation of cathode feedback prior to the application of blanking prevents significant distortion, deformation or distortion of the cathode feedback current sensed by the AKB sensing circuit 19 of the video processor 13.

Description

DISPLAY SYSTEM COMPRISING A VEDEO PROCESSOR}

Background of the Invention

Automatic cathode ray tube (CRT) black level stabilization is typically achieved by inserting bias voltages into drive signals near the video black level during the vertical blanking interval. In a feedback system, the relevant DC biases of the drive signals are adjusted to achieve the same CRT red, green and blue (RGB) cathode currents near the video black level. In general, these bias voltages are the top overscanned portion of the display and are not visible. However, in display modes where vertical deflection is understood, such as when a 16: 9 aspect ratio image is displayed on a 4: 3 display, these bias voltages are visible and confused.

Field of invention

The present invention relates to a cathode ray tube (CRT) or similar display systems, in particular to a display system with automatic CRT black level stabilization, so-called automatic kinescope bias (AKB) applying a feedback loop.

1 is a schematic diagram of a conventional display system.

2 is a schematic diagram of a display system according to the invention;

3 shows another embodiment of a schematic diagram of a display system according to the present invention;

Summary of the Invention

The present invention relates to a display system that prevents bias voltages from becoming visible. The invention is defined by the independent claims. Dependent claims define preferred embodiments.

According to a first aspect of the invention, there is provided a display system as generated in an opening paragraph, wherein the system is

A video processor for generating red, green and blue drive signals each having a red output bias, a green output bias and a blue output bias corresponding to a respective black level of the respective drive signals,

Cathode ray tube (CRT) with red, green and blue cathodes,

A drive stage coupled to receive red, green and blue output biases for driving red, green and blue cathodes,

A CRT feedback current replacement circuit for generating a cathode feedback replacement current corresponding to each of the black levels and receiving red, green and blue output biases coupled to a drive stage to supply the replacement cathode black current to a video processor, and

And a blanking circuit coupled to the drive stage for selectively generating vertical blanking signals for blanking the outputs of the drive stage when the cathode feedback replacement current is generated.

The system uses an alternative circuit called a simulation circuit to generate feedback directly from the drive signals of the video processor. In this way a feedback loop to stabilize the black level of the cathode ray tube maintains operation without requiring feedback from the drive stage.

Thus, vertical blanking can be applied to the drive stage to ensure that the CRT completely cuts off despite the presence of an output bias at the inputs of the drive stage. Thus, for example, in the case of vertical underscan, the visibility of the output biases is avoided. This feature, which uses a feedback current replacement circuit in combination with vertical blanking during the presence of output biases, is not permanently activated when the display system is operating. If the display system is in an operating mode in which vertical underscanning occurs, it is available to operate the feature.

Thus, the present invention provides a display system having a means for alternatively replacing another cathode feedback current source, such as during vertical underscanning conditions, without optionally using AKB or in other words AKB.

These and other aspects of the invention will be apparent and shown with reference to the drawings.

Detailed description of the invention

Referring to Fig. 1, a schematic diagram of a conventional display system 1 with an automatic kinescope bias (AKB) is shown. The display system 1 monitors the current feedback on the line 2 which is supplied to the current feedback input terminal 5 during the reference pulse interval, and the red output bias 4R, the green output bias 4G to maintain the same cathode current. ), And a video processor integrated circuit (IC) 3 that adjusts the blue output bias 4B. The display system 1 further comprises a CRT drive stage 6 with a plurality of CRT drive amplifiers 6a, 6b, 6c which are operational amplifiers. Each CRT drive amplifier 6a, 6b, 6c has three outputs on line 8 ₁ , 8 ₂ , 8 ₃ . The output on line 8 ₁ of each CRT drive amplifier 6a, 6b, 6c drives red, green and blue CRT cathodes RC, GC and BC, respectively, and sinks current. The line 8 ₂ on-output of each CRT drive amplifier 6a, 6b, 6c supplies the cathode feedback current to the AKB sensing circuit 9 of the video processor integrated circuit (IC) 3 on line 2. . The output on line 8 ₃ of the CRT drive amplifiers 6a, 6b, 6c is coupled to the first terminal of each one of the feedback resistors R7, R8, R9.

The CRT drive amplifiers 6a, 6b, 6c each have a resistor or impedance R4, R5 and R6 coupled to the first input terminal of the CRT drive amplifiers 6a, 6b, 6c. In addition, the second terminal of the feedback registers R7, R8 and R9 is coupled to the first input terminal of the CRT drive amplifiers 6a, 6b and 6c, respectively. In addition, each of the CRT drive amplifiers 6a, 6b, 6c has a second input terminal which receives on the line 7 a vertical blanking signal with a reference pulse during the reference pulse interval.

Referring to Fig. 2, the display system of the present invention is represented by the number ten. The display system 10 generally applies a blanking (vertical blanking signal) in order to prevent (1) the bias voltage from being visible and (2) a CRT feedback current replacement circuit 20 disposed before the drive stage 16. By replacing the conventional cathode feedback current from the output of the drive stage 16 with the cathode feedback replacement current from), it eliminates the visible bias voltage of the drive signals when the vertical deflection is underscanned. The replacement current simulates a conventional cathode feedback current, so called simulated cathode feedback current. The CRT feedback current replacement circuit 20 provides feedback from a position prior to the drive stage 16 such that a vertical blanking signal without a reference pulse on the line 17 causes the drive stage 16 to not severely distort, deform or distort the cathode feedback current. ) Can be applied. This vertical blanking signal is supplied by the blanking circuit 17 ₁ and can be selectively supplied only in the case of vertical underscanning. The blanking circuit is an independent circuit or part of another circuit. In an exemplary embodiment, the cathode feedback replacement circuit is directly from the respective output bias, green 14G, and blue drive signals 14B of the red 14R supplied by the video processor integrated circuit (IC) 13. Simulated.

The CRT feedback current replacement circuit 20 includes a current mirror 22, a red transistor Q1 having a base coupled to the red drive signal 14R, and a green transistor Q2 having a base coupled to the green drive signal 14G. And a blue transistor Q3 having a base coupled to the blue drive signal 14B. Current mirror 22 includes transistors Q4 and Q5 with the collector of transistor Q4 and with bases coupled to the collector. Emitters of the transistors Q4 and Q5 are coupled to the supply voltage Vcc of the IC 13. The collectors of red transistor Q1, green transistor Q2 and blue transistor Q3 are all coupled to the collector and base of transistor Q4. Emitters of red transistor Q1, green transistor Q2, and blue transistor Q3 are coupled to ground through respective emitter transistors or impedances R1, R2, R3.

The CRT feedback current replacement circuit 20 further includes a current sink transistor Q10 having a collector connected to the transistor Q5 collector of the current mirror 22 at node A. At node A, net current is delivered to current feedback input terminal 15 of video processor integrated circuit (IC) 13. The base of transistor Q10 is coupled to ground and the emitter has a resistor or impedance R12 coupled to voltage Vee. As can be appreciated, collector currents I5 and I10 of transistors Q5 and Q10 supply net current to node A which defines the cathode feedback replacement current of CRT feedback current replacement circuit 20. The cathode feedback replacement current is transferred from node A to the current feedback input terminal 15 of the video processor integrated circuit (IC) 13 and sensed by the AKB sensing circuit 19. It is noted that AKB is known as CRT cutoff stabilization and black level stabilization.

In operation, the collector current of transistors Q1, Q2 and Q3 generated by sequential reference levels during vertical retrace and mirrored through transistors Q4 and Q5 of current mirror 22 is a current sink transistor. It is only slightly larger than the current sinked by Q10. By sinking current through transistor Q10, transistors Q1, Q2 and Q3 remain active at any time with relatively small changes in their respective collector currents, providing a stable characteristic, especially for the base emitter voltage. In other words, the output current from transistor Q5 of current mirror 22 is sinked by transistor Q10. Collector currents from transistors Q5 and Q10 are in the milliampere range. However, the current towards the current feedback input terminal 15 is in the microamperes range. Thus, when current I5 is slightly larger than current I10, the loop is stabilized to minimize the change in base emitter junction of transistors Q1 to Q3.

In an exemplary embodiment, the CRT "cut off" voltage is for example +180.0 volts (when the first grid of the CRT is connected to ground). However, as is known, at a voltage of approximately + 179.9V, some current is obtained so that the CRT causes illumination. The vertical blanking signal without reference pulse is supplied to the CRT drive amplifiers 16a, 16b, 16c on line 17 to prevent the bias voltage from being visible on the display 35, especially in display mode where the vertical deflection is underscanned. .

Referring to the schematic diagram of the display system 10 of FIG. 2, the outputs on the line 18 ₁ of each CRT drive amplifier 16a, 16b, 16c show the respective red, green and blue CRT cathodes RC, GC and BC. Drive to sink the current in the display 35. The AKB output on line 18 ₂ of each CRT drive amplifier 16a, 16b, 16c is such that when the feedback current replacement circuit 20 must provide feedback (e.g., in the vertical underscan mode of operation), FIG. It is coupled to ground as shown. If the AKB output is used in another mode of operation, this output should be coupled to the current feedback input terminal 15 as shown in another embodiment shown in FIG. The output on line 18 ₃ of each CRT drive amplifier 16a, 16b, 16c drives the respective output of feedback resistors R7, R8, R9.

3, another embodiment of a schematic diagram of a display system according to the present invention is shown. The display system 100 converts the cathode feedback current from the driving stage 116 or the cathode feedback replacement current from the CRT feedback current replacement circuit 120 into the current feedback input terminal 115 of the video processor integrated circuit (IC) 130. And an optional switching circuit 140 for selectively supplying to the. Since the CRT feedback current replacement circuit 120 is essentially the same as the CRT feedback current replacement circuit 20 of FIG. 2, further discussion will be made except as it relates to the optional switching circuit 140.

With reference to the optional switching circuit 140, an AKB "on" or "off" signal is passed on the line 142 through the resistor R23 to the base of the transistor Q12 and the AKB "on" signal is approximately 5V and The AKB "off" signal is nearly 0V. On line 142 an AKB “on” or “off” signal is transmitted to the base of transistor Q13 on line 144 and the base of transistor Q9 on line 146. The base of transistor Q11 is coupled to the base of transistor Q8. Emitters of transistors Q11 and Q12 are coupled together at Node B, which receives a second output from CRT drive amplifiers 116a, 116b, 116c on line 118 ₂ . The current on line 118 ₂ supplies the cathode feedback current to the AKB sensing circuit 119 via the current feedback input terminal 115. The collector of transistor Q12 is connected to a negative voltage -Vee.

Transistors Q8 and Q9 have emitters connected to node C coupled to transistor Q5 collector of current mirror 122. The collector of transistor Q9 is coupled to the collector and transistor A of transistor Q10. The collector of Q8 is connected to ground. The base of transistor Q11 is coupled to the base of base transistor Q8 which is connected to supply voltage Vcc at node D via resistor R10 on line 152. The other terminal of resistor R12 is coupled to negative voltage Vee. The collector of transistor Q13 is coupled to Vcc on line 150. In this embodiment, the base of transistor Q10 is coupled to the base of transistor Q8 via resistor R11, and register R11 is in series and between registers R10 and R13. . Resistor R13 is coupled to ground.

In operation, when an AKB “on” signal is provided to line 142, CRT feedback current replacement circuit 120 is selectively disabled and the collector of transistor Q11 is CRT drive amplifiers 116a on line 118 ₂ . 116b and 116c to deliver a cathode feedback current to the current feedback input terminal 115 of the video processor integrated circuit (IC) 130 via the readback line 148. This cathode feedback current is sensed by the AKB sensing circuit 119.

On the other hand, when an AKB "off" signal is provided on line 142, CRT feedback current replacement circuit 120 is enabled and passes from transistor Q5 to transistor Q9 and transistor Q10 at node A. The net collect current delivers the cathode feedback replacement current to the current feedback input terminal 115.

Transistors Q11 and Q12 as well as transistor pairs Q8 and Q9 are optionally "on" and "off" biased. Thus, when an AKB "on" signal is provided, transistor Q11 is on, transistor Q12 is off, transistor Q8 is on, transistor Q9 is off and transistor Q13 is transistor Q10. Off). Therefore, the resulting cathode feedback current at Node B is delivered to current feedback input terminal 115 via line 148.

However, when the AKB "off" signal is provided, transistor Q11 is off, transistor Q12_ is on, transistor Q8 is off, and transistor Q9 is on. Transistor Q10 is also turned on through transistor Q13. Therefore, the cathode feedback replacement current at node A is the net collector current through transistor Q9 and transistor Q10 from the collector of transistor Q5. This net collector current is supplied to the current feedback input terminal 115.

In this embodiment, the CRT feedback current replacement circuit 120 only needs to be activated during the underscan mode of operation without limitation when the 16: 9 aspect ratio is displayed on a 4: 3 display. Otherwise, there is no reason to invalidate AKB with different cathode feedback current sources during different modes of underscan node.

Referring to the schematic diagram of the embodiment of FIG. 3, the output on line 118 ₁ of each CRT drive amplifier 116a, 116b, 116c drives respective red, green and blue CRT cathodes RC, GC and BC and displays ( Sink the current of 135). Each CRT drive amplifier 16a, 16b, 16c drives resistors or impedances R4, R5, and R6 coupled to first input terminals of the CRT drive amplifiers 116a, 116b, 116c, respectively. In addition, feedback registers R7, R8 and R9 are coupled to the first input terminal of each CRT drive amplifier 116a, 116b, 116c. In addition, each of the CRT drive amplifiers 116a, 116b, 116c has a second input terminal that receives from the blanking circuit 117 a vertical blanking signal that does not have reference pulses for a reference pulse interval on line 117. Note that the vertical blanking signal without reference pulse is applied on lines 17 and 117 only in the AKB off mode.

In mode AKB, the second input terminal receives blanking signals with reference pulses that prevent blanking while the output bias is provided.

Many variations of the invention will be apparent to those skilled in the art in light of the above detailed description. Accordingly, this specification is intended to show those skilled in the art the best mode of carrying out the invention, which is intended to be illustrative only. The details of the structure can be changed substantially without departing from the invention and the exclusive use of all modifications falling within the scope of the appended claims is reserved.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "compiling" does not exclude other elements or steps than those listed in the claims. The word "er" or "un" does not exclude the presence of multiple elements. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In some means listed in the device claims above, some of these means are realized by the same item and one of the hardware. The simple fact that any method is limited to mutually dependent claims does not indicate that a combination of these methods cannot be used preferably.

Claims (7)

In the display system 10 (100), Red, green and blue drive signals 14R, 14G and 14B with respective red output bias, green output bias and blue output bias corresponding to respective black levels of respective drive signals 14R, 14G and 14B. A video processor 13; Cathode ray tube (CRT) 35; 135 with red, green and blue cathodes (RC, GC, BC); A drive stage (16; 116) coupled to receive the red, green and blue output biases for driving red, green and blue cathodes (RC, GC, BC); The red, green and blue outputs coupled to drive stages 16 and 116 to generate cathode feedback replacement currents corresponding to respective black levels and to supply the replacement cathode feedback currents to video processor 13 and 130; A CRT feedback current replacement circuit (20; 120) for receiving the biases; And A blanking circuit (17; 117) coupled to the drive stage (16; 116) for selectively generating a vertical blanking signal for blanking the outputs of the drive stage (16; 116) when the cathode feedback replacement currents are generated. , Display system. The video processor (13; 130) of claim 1 includes an automatic kinescope bias (AKB) sensing circuit (19; 119) and the cathode feedback alternative currents are sensed by the AKB sensing circuit (19; 119). , Display system. 2. The method according to claim 1, wherein the cathode feedback currents from the drive stage (16; 116) and the CRT feedback current replacement circuit (20; 120) are prevented to prevent the cathode feedback currents from becoming visible during vertical underscanning conditions. And a switching circuit (140) for selectively switching between cathode feedback replacement currents. 2. The CRT feedback current replacement circuit (20; 120) of claim 1 further comprising: a current mirror (22; 122) having a first transistor (Q4) and a second transistor (Q5); A red output bias transistor (Q1) having a base receiving the red output bias, a collector coupled to a first transistor (Q4) collector of a current mirror (22; 122), and an emitter coupled to a first resistor (R1); A green output bias transistor (Q2) having a base for receiving the green output bias, a collector coupled to a first transistor (Q4) collector of a current mirror (22; 122), and an emitter coupled to a second resistor (R2); A blue output bias transistor (Q3) having a base receiving the blue output bias, a collector coupled to a first transistor (Q4) collector of a current mirror (22; 122), and an emitter coupled to a third resistor (R3); And A current sink transistor Q10 having a base coupled to a bias voltage, an emitter coupled to a fourth resistor R12 and a collector coupled to the collector of the second transistor Q5, and comprising a current sink transistor Q10. And the net current of the collector current of the second transistor (Q5) collector current provides the cathode feedback alternative current. 5. The cathode of claim 4, wherein the cathode feedback currents from the drive stage 16; 116 and the cathode from the CRT feedback current replacement circuit 20; 120 so that the red, green and blue output biases are not visible during vertical underscanning conditions. And a switching circuit (140) for selectively switching between feedback alternative currents. The method of claim 5, wherein the switching circuit 140, A first transistor pair (Q11, Q12) with alternatingly biased transistors for receiving the cathode feedback current and a switching signal from the CRT output drive stage (16; 116), wherein the first transistor pair (Q11, Q12 includes: the first pair of transistors (Q11, Q12) for selectively delivering the cathode feedback current to a video processor (13; 130); A second pair of transistors (Q8, Q9) having alternatingly biased transistors disposed between the collector of the second transistor (Q5) and the collector of the current sink transistor (Q10) and receiving the switching signal; And And a switching transistor (Q13) for receiving said switching signal and selectively turning off a current sink transistor (Q10). A method of blanking the red, green and blue output biases of drive signals on a cathode ray tube (CRT) display 35; Generating, by a video processor (13; 130), the red output bias, the green output bias and the blue output bias; Replacing cathode feedback currents at the video processor (13; 130) with cathode feedback replacement currents obtainable from the red, green and blue output biases through a CRT feedback current replacement circuit (20; 120); Generating a vertical blanking signal for a time period during which the cathode feedback replacement currents are provided; And Blanking the outputs of a drive stage (16; 116) driving a CRT display (35; 135) with the vertical blanking signal.